The invention relates to a radio frequency ion beam source comprising an ioniser vessel which can be charged with the particular working gas to be ionised, in particular, gaseous, condensable metal vapours and metal compounds; a coil connected to a radio frequency source for generating a plasma in the ioniser vessel, with the plasma arising through inductively stimulated discharge; and also a beam forming system with several extraction grids.
The technology of surface treatment and in particular the manufacture of thin layers has become very significant in recent years, particularly with regard to the industrial application of such processes. There are nowadays numerous processes for the manufacture or preparation of thin layers and for the treatment of material surfaces. They all require either reduced pressure or vacuum in the processing chamber and are thus carried out in vacuum systems.
Some very well known processes relate to vaporisation by Joule heating in furnaces, boats, crucibles etc. either by electric heating or by electronic or ion bombardment. Other processes use vaporisation produced by means of an anodic or cathodic arc or also by eddy current heating of conductive material in an induced AC field. Mention should also be made of large area sublimation on cathodes using various cathode sputtering arrangements with and without magnetic enhancement of the ionisation in the DC or AC glow discharge.
The known and customary vaporisation sources deliver atoms and ions for the condensation on the substrate which have a broad distribution of kinetic energies of the particles. This is a problem because the highly energetic particles cause damage rather than the generally desired uniform condensation, which results in faultfree crystal growth. The damage caused can take the form of crystal splitting, crystal destruction or decomposition of the surface, in a similar form to cathode sputtering. On the other hand the incident particles of low energy frequently do not attain the required kinetic energy at the surface for an orderly incorporation into a crystal grid.
These energies are frequently not sufficient in order to obtain the desired bond strength of the coating in the boundary surface between the substrate and the layer. In some cases a high energy of the particles is required in the coating beam in order to increase the surface energy of the substrate, when the substrate temperature has to be kept low for certain reasons, or when the heat exchange between the substrate and the uppermost condensation plane is deficient.
Radio frequency ion sources of the initially named kind are also known (see EP-A No. 2 0 261 338 and DE-A No. 1 37 08 716) in which the r.f. coil is arranged outside of the respective ioniser vessel and specially formed ion extraction systems are used. Such ion beam sources make it possible to generate only simply charged ions, i.e. only a single monoenergetic beam peak, can also be used with reactive gases, have a robust and simple construction and also a simple supply regulation unit, they are also able to satisfy the practical requirement placed on operational reliability and working life.
It is however not possible with the known radio frequency ion beam sources to satisfy the requirements which arise in practice for intensive beams of variable ion energy right down to extremely low values, and in particular the requirement to also generate metal ions.